Exhaust gas recirculation

ABSTRACT

A control valve assembly responsive to exhaust back pressure controls recirculation of exhaust gases from the intake manifold exhaust crossover passage to the intake manifold induction passages.

United States Patent 1191 Bolton Mar. 26, 1974 1 EXHAUST GAS RECIRCULATION 2,851,021 9/1958 Covone 123/119 A 3,507,260 4/1970 Walker 123/119 A [75] P Sterlmg 3,662,722 5/1912 Sarto 123/119 A 3,641,989 2/1972 Aill 123/119 A Assignee: General Motors Corporation 3,241,536 3/1966 Falzone 123/119 A Detroit, Mich.

- Primary ExaminerWendell E. Burns d: 1 1972 [22] F116 Apr 9 Attorney, Agent, or F1rm-C. K. Veenstra [21] Appl. No.: 245,587

52 us. Cl 123/119 A [57] ABSTRACT [51] Int. Cl. F02m 25/06 A control valve assembly responslve to exhaust back [58] Field of Search 123/119 A, 60/278 pressure controls recirculation of exhaust gases from the intake manifold exhaust crossover passage to the [56] g gfi'iz gif intake manifold induction passages.

1,051,690 1/1913 Colwell 123/119 A 20 Claims, 9 Drawing Figures EXHAUST GAS RECIRCULATION SUMMARY OF THE INVENTION This invention relates to exhaust gas recirculation in an internal combustion engine and more particularly to a novel method and means for controlling exhaust gas recirculation.

Recirculation of exhaust gases has been developed as a method for reducing formation of oxides of nitrogen during the combustion process in an internal combustion engine. In general, it is desired to recirculate the exhaust gases at a rate proportional to the rate at which combustion air flows into the engine, and valves responsive to induction passage vacuum or throttle position have been utilized for this purpose.

It also has been recognized that, if exhaust gases were recirculated through an orifice into a region of substantially atmospheric pressure in the engine air induction system, variations in exhaust back pressure would cause the exhaust gas recirculation rate to be proportional to the combustion air flow rate. However, such a system would require that the exhaust gases pass through at least a portion of the carburetor.

This invention provides a novel method and means for utilizing the exhaust back pressure to recirculate exhaust gases at} rate proporti 1a l to air flow and in a manner by which recirculation of exhaust ga ses through the carburetor is avoided. In employing this invention, an exhaust gas recirculation passage is provided which extends from the engine exhaust passage to the engine air induction passage at a point downstream of the engine throttle. An orifice is provided in the recirculation passage, and a valve disposed downstream of the orifice is operated to create a zone of substantially constant pressure in the passage irrespective of the wide variations in exhaust back pressure and induction passage vacuum. The pressure in the zone may be maintained either above or below atmospheric pressure, and the rate of flow of exhaust gases into and through the zone will be proportional to the rate of induction air flow.

Various embodiments of the valve employed to achieve this end are depicted herein, the details of which as well as other objects and advantages of this invention are set forth in the remainder of the specification and in the drawings.

SUMMARY OF THE DRAWINGS FIG. 1 is a top plan view of an internal combustion engine inlet manifold having induction and exhaust gas crossover passages, an insert plate having an exhaust gas recirculation passage mounted on the manifold, and an exhaust gas recirculation control valve assembly mounted on the insert plate;

FIG. 2 is a sectional view along line 2-2 of FIG. 1 showing the induction, exhaust gas crossover, and exhaust gas recirculation passages and also showing the throttle body portion of a carburetor mounted on the insert plate;

FIG. 3 is an enlarged sectional view, in elevation, of one embodiment of the control valve assembly, taken generally along line 3-3 of FIG. 1;

FIG. 4 is a sectional view, in elevation, of another embodiment of the control valve assembly which may be connected to the insert plate by appropriate piping;

FIG. 5 is a sectional view, in elevation, of a further embodiment of the control valve assembly which also may be connected to the insert plate by appropriate piping;

FIG. 6 is a sectional view, in elevation, of an additional embodiment of the control valve assembly as it would be mounted on the insert plate;

FIG. 7 is a sectional view, in elevation, of yet another control valve assembly, also showing how it may be mounted on the insert plate and schematically showing an additional control mode which may be utilized with this embodiment;

FIG. 8 is a sectional view, in elevation, of another embodiment of the control valve assembly as it would be mounted on the insert plate; and

FIG. 9 is a sectional view, in elevation, of another embodiment of the control valve assembly as it would be mounted on the insert plate.

The improved embodiment of this invention shown in FIG. 3 was invented by James .I. Gumbleton and Paul B. Kuehl and is specifically claimed in commonly assigned U.S. Pat. application Ser. No. 245,590 filed Apr. 19, 1972. The improved embodiment of this invention shown in FIG. 8 was invented by Paul B. Kuehl and is specifically claimed in commonly assigned U.S. Pat. application Ser. No. 242,420 filed Apr. 10, 1972. The FIG. 7 and 8 embodiments are improved embodiments of the invention of William L. Kingsbury claimed in commonly assigned U.S. Pat. application Ser. No. 244,378 filed Apr. 17, 1972. The FIG. 7 and 9 embodiments make use of the invention of Edward G. Day and Ernst L. Ranft claimed in commonly assigned U.S. Pat. application Ser. No. 220,036 filed Jan. 24, I972. The FIG. 9 embodiment also makes use of an invention of Ernst L. Ranft and William F. Thornburgh claimed in commonly assigned U.S. Pat. application Ser. No. 314,569 filed Dec. 13, I972.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 2, the combustion air induction passages for the engine are formed in part by an intake manifold 10 which has a pair of vertical primary riser bores 12 and 14 and a pair of vertical secondary riser bores 16 and 18. Riser bores 12 and 16 open to an upper horizontal plenum 20 connected forwardly (leftwardly as viewed in FIG. 1) to a pair of transverse runners 22 and 24 and connected rearwardly (rightwardly as viewed in FIG. 1) to another pair of transverse runners 26 and 28. Similarly, riser bores 14 and 18 open to a lower horizontal plenum 30 connected forwardly to a pair of transverse runners 32 and 34 and rearwardly to another pair of transverse runners 36 and 38.

Intake manifold 10 also has an exhaust crossover passage 40 which extends transversely from the left-hand side of manifold 10 beneath plenums 20 and 30 and receives a portion of the exhaust gases discharged from the engine combustion chambers.

An insert plate 42 is secured on manifold 10 and has primary riser bores 44 and 46 and secondary riser bores 48 and 50 which meet, respectively, riser bores 12, 14, l6, 18 of manifold 10.

A carburetor 52 is secured on insert plate 42 and has primary throttle bores 54 and 56 which meet, respectively, primary riser bores 44 and 46 of insert plate 42. Carburetor 52 also has secondary throttle bores (not shown) which meet secondary riser bores 48 and 50 of insert plate 42.

A bore 58 in manifold leads upwardly from exhaust crossover passage 40 to the first portion 60 of an exhaust recirculation passage formed in insert plate 42. The first portion 60 of the exhaust recirculation passage leads through a control valve assembly 62 to a second portion 64 of the exhaust recirculation passage. This second portion 64 divides into a pair of branches 66 and 68 which lead to the primary riser bores 44 and 46 in insert plate 42.

It should be appreciated that both portions 60 and 64 of the exhaust recirculation passage may be integrated in manifold 10 rather than in separate insert plate 42.

Referring now to the FIG. 3 embodiment 62a of control valve assembly 62, a valve body 70 has an inlet 72 receiving exhaust gases from first portion 60 of the exhaust recirculation passage and an outlet 74 discharging exhaust gases to second portion 64 of the exhaust recirculation passage.

Coaxial upwardly facing valve seats 76 and 78 are formed in valve body 70 to control flow of exhaust gases from inlet 72 to outlet 74. An orifice member 80 is disposed across inlet 72.

A pair of valve members 82 and 84 are associated with valve seats 76 and 78 to control exhaust gas flow therethrough. It will be noted that the opening 86 (about which valve seat 76 is formed) is smaller than the opening 88 (about which valve seat 78 is formed) and that valve member 82 is smaller than valve member 84 and may pass through opening 88 for ease of assembly.

Valve members 82 are formed on or otherwise secured to a hollow stem 90 which is open at its lower end 92 and which has lateral openings 94 above valve member 84.

The upper end of stem 90 is guided in the central aperture 96 of a web 98 forming part of valve body 70 and is secured to the top plate 100 of a resilient metal bellows 102.

In operation, the pressure in the zone 104 just downstream of orifice 80 is transmitted through hollow stem 90 to the chamber 106 above upper valve seat 78 and thence through apertures 108 in web 98 to the interior of bellows 102. As shown here, the exterior of bellow's 102 is exposed to atmospheric pressure. Upon an increase in pressure in zone 104, bellows 102 expands to lift valve stem 90 and displace valve members 82 and 84 away from valve seats 76 and 78. Exhaust gases are then recirculated from first portion 60 of exhaust gas recirculation passage past orifice 80, through valve seat 76 and through stem 90, lateral openings 94, chamber 106 and valve seat 78, to second portion 64 of the exhaust gas recirculation passage. Upon a decrease in pressure in zone 104, bellows 102 contracts to lower stem 90 and displace valve members 82 and 84 toward valve seats 76 and 78, thus reducing recirculation of exhaust gases. Control valve assembly 62a is thus effective to maintain a substantially constant pressure in zone 104 just downstream of orifice 88.

The back pressure created in the exhaust passages such as 40 of an internal combustion engine is generally proportional to the square of the rate of combustion air flow through the engine induction passages. The rate of flow of exhaust gases from an exhaust passage such as first portion 60 of the exhaust recirculation passage through an orifice such as into a zone such as 104 of substantially constant pressure is generally proportional to the square root of the exhaust back pressure. Thus the rate at which exhaust gases are recirculated is generally proportional to the rate at which combustion air flows to the engine. While for simplicity this specification may refer to the exhaust back pressure as being proportional to the engine air flow rate and to the exhaust gas recirculation rate, it should be recognized that back pressure actually is proportional to the square of the air flow and exhaust gas recirculation rates.

It will be noted that bellows 102 may be designed to maintain any desired pressure in zone 104. If zone 104 is to be maintained at a pressure above atmospheric, bellows 102 is designed to bias valve members 82 and 84 toward valve seats 76 and 78; if zone 104 is to be maintained at a pressure below atmospheric, bellows 102 is designed to bias valve members 82 and 84 away from valve seats 76 and 78. If desired, spring means may be employed to assist the inherent elasticity of bellows 182.

It also will be noted that valve seat 76 and valve member 82 are disposed on the outlet side of opening 86 while valve member 84 and valve seat 78 are disposed on the inlet side of opening 88. Thus the upper surface of valve member 84 and the lower surface of valve member 82 are subjected to the pressure of zone 104 while the lower surface of valve member 84 and the upper surface of valve member 82 are subjected to the pressure in outlet 74. The pressures acting on valve members 82 and 84 are thereby balanced, and thus control valve assembly 62a is substantially unaffected by pressures acting on valve members 82 and 84.

FIG. 4 shows another embodiment 62b of control valve assembly 62. It comprises a valve body 110 having an inlet 112 for receiving exhaust gases from first portion 60 of the exhaust recirculation passage, an outlet 114 for discharging exhaust gases to second portion 64 of the exhaust recirculation passage, an orifice member 116 disposed in inlet 112, and a web 1118 providing a pair of coaxial openings 120 and 122 about which a pair of upwardly facing valve seats 124 and 126 are formed. A stem 128 carries valve members 130 and 132 and extends through an aperture 134 in a web 136 to a pressure responsive diaphragm 138. Opening 120 and its associated valve member 130 are smaller than opening 122 and its associated valve member 132 so that valve member 130 may pass through opening 122 for ease of assembly.

In operation, the pressure in zone 140 just downstream of orifice member 116 is applied through an aperture 142 in web 136 to the chamber 144 beneath diaphragm 138. The upper surface of diaphragm 138 is shown here as subjected to atmospheric pressure. Upon an increase in zone 140, diaphragm 138 is lifted against the bias of spring 146 to displace valve members 130 and 132 from valve seats 124 and 126, thus permitting increased recirculation of exhaust gases from first portion 60 of the exhaust gas recirculation passage through inlet 112, orifice member 116, zone 140, valve seats 124 and 126, and outlet 114 to second portion 64 of the exhaust gas recirculation passage. Upon a decrease in pressure in zone 140, spring 146 presses diaphragm 138 downwardly which displaces valve members 130 and 132 toward valve seats 124 and 126 to reduce recirculation of exhaust gases. Thus control valve assembly 62b is effective to maintain a substantially constant pressure in zone 140.

As described above, embodiment 62b of the control valve assembly maintains the pressure in zone 140 above atmospheric pressure, spring 146 acting as a compression spring. However, if spring 146 were designed as a tension spring, or if spring 146 were disposed below diaphragm 138 rather than above diaphragm 138, embodiment 62b would be effective to maintain the pressure in zone 140 at a subatmospheric value. The same modifications could be made to other embodiments of control valve assembly 62 shown herein.

It will be noted that in embodiment 62b, as in embodiment 62a, valve member 130 and its associated valve seat 124 are disposed on the outlet side of opening 120 while valve member 132 and its associated valve seat 126 are disposed on the inlet side of opening 122. The pressures acting on the valve members 130 and 132 are thereby balanced, and embodiment 62b is substantially unaffected by pressures acting on valve members 82 and 84.

FIG. 5 shows further embodiment 62c of control valve assembly 62. It comprises a valve body 148 having an inlet 150 for receiving exhaust gases from first portion 60 of the exhaust recirculation passage, an outlet 152 for discharging exhaust gases to second portion 64 of the exhaust recirculation passage, an orifice member 154 in inlet 150, and an opening 156 which has an upwardly facing valve seat 158 formed about the inlet side thereof. A valve member 160 is associated with valv seat 158 and is mounted or formed on a stem 162 which slides in a bushing 164 mounted in the central aperture 166 of a web 168. Stem 162 is operated by a pressure responsive diaphragm 170 and is biased downwardly by a spring 171. The pressure in zone 172 just downstream of orifice member 154 is transmitted through an aperture 174 in web 168 to the chamber 176 beneath diaphragm 170, while the upper surface of diaphragm 170 is shown as exposed to atmospheric pressure. Diaphragm 170 operates valve 160 to maintain a substantially constant pressure in zone 172.

Valve stem 162 has an extension 178 connected to a second diaphragm 180. The effective area of diaphragm 180 is equal to the area of valve member 160 exposed to the pressure in outlet 152 through opening 156. The pressure in outlet 152 is transmitted through a passage 182 in valve stem 162 to the chamber 184 above diaphragm 180.

Thus it will be appreciated that the depression in outlet 152 tending to pull valve member 160 downwardly is offset by the depression in chamber 184 acting on diaphragm 180 to lift valve member 160; embodiment 62c is therefore unaffected by variations in induction passage vacuum.

FIG. 6 shows an additional embodiment 62d of control valve assembly 62. It comprises a valve body 186 having an inlet 188 receiving exhaust gases from first portion 60 of the exhaust recirculation passage and an outlet 190 discharging exhaust gases to second portion 64 of the exhaust recirculation passage. An orifice member 192 is disposed in inlet 188, and an opening 194 has a downwardly facing valve seat 196 formed about its inlet side. A valve member 198 is secured by a stem 200 to a pressure responsive diaphragm 202 which is biased upwardly by a spring 204. A hose 206 subjects the chamber 208 above diaphragm 202 to the pressure in the zone 210 between orifice member 192 and valve seat 196, while the lower surface of diaphragm 202 is shown as subjected to atmospheric pressure. Embodiment 62d also is effective to maintain a substantially constant pressure in zone 210.

A piston 212 and a bushing 214 are rigidly connected between diaphragm 202 and valve member 198. The face 216 of piston 212 and the portion of valve member 198 exposed through opening 194 have equal areas and are equally exposed to the pressure in outlet 190. Piston 212 thereby offsets the effect of induction manifold vacuum on valve member 198.

FIG. 7 shows yet another embodiment 622 of control valve assembly 62. It comprises a valve body 218 having an inlet 220 receiving exhaust gases from first portion 60 of the exhaust recirculation passage, an outlet 222 discharging exhaust gases to the second portion 64 of the exhaust recirculation passage. An orifice member 224 is disposed across inlet 220, and a valve seat 226 is formed about the outlet side of a fitting defining an opening 227. A valve member 228 associated with valve seat 226 is connected by a stem 230 to a pressure responsive diaphragm 232.

The pressure in the zone 234 between orifice member 224 and valve seat 226 is applied through a hose 236 to a chamber 238 below a diaphragm 240, while the upper surface of diaphragm 240 is shown as exposed to atmospheric pressure. Diaphragm 240, biased downwardly by a spring 242, is lifted upon an increase in pressure in zone 234. A pilot valve 244, connected by a stem 246 to diaphragm 240, controls an air bleed orifice 248 which opens into a vacuum chamber 250. A fitting 252 on chamber 250 is connected through hoses 254 and 256 to a source of vacuum such as that in carburetor 52 below the throttles 258 or that in outlet 222. A second fitting 260 on chamber 250 is connected by a hose 262 to the chamber 264 above diaphragm 232.

In operation, diaphragm 240 is raised against the bias of spring 242 upon an increase in pressure in zone 234, and valve member 244 reduces the effective area of orifice 248. This increases vacuum in chamber 250, and diaphragm 232 is raised against the bias of a spring 266. Thus valve member 228 is displaced from valve seat 226 to permit increased recirculation of exhaust gases. Upon a decrease in pressure in zone 234, spring 242 depresses diaphragm 240, and valve member 244 permits increased flow through orifice 248. The resulting reduction in vacuum in chamber 250 is transmitted to chamber 264, and spring 266 lowers diaphragm 232 to displace valve member 228 toward valve seat 226, thus reducing recirculation of exhaust gases. Thus valve member 228 is operated to maintain the pressure in zone 234 at a substantially constant value.

If desired, a valve 268, responsive to temperature or some other engine or vehicle operating condition, may be disposed between hoses 254 and 256 to control application of vacuum to chamber 264 and thus to superimpose a supplemental control on recirculation of exhaust gases.

It also will be appreciated that embodiment 62e may be tailored so that valve member 228 engages valve seat 226 to prevent recirculation of exhaust gases under wide open throttle operating conditions when the vacuum transmitted through hose 256 is very low.

It will be noted that an additional control surface 269 may be employed on valve member 244 to further control the supply of vacuum to chamber 250. And it should be appreciated that hose 254 may be connected to fitting 260 and hose 262 to fitting 252 if such should be desired.

FIG. 8 shows another embodiment 62f of control valve assembly 62 which operates in a manner similar to that of embodiment 62c. Embodiment 62fcomprises a valve body 270 having an inlet 272 receiving exhaust gases from first portion 60 of exhaust recirculation passage and an outlet 274 discharging exhaust gases to the second portion 64 of the exhaust recirculation passage. An orifice member 276 is disposed across inlet 272, and a downwardly facing valve seat 278 is formed about the inlet side of an opening 279. A valve member 280 associated with valve seat 278 is formed on a ho]- low stem 282 carried by a pressure responsive diaphragm 284 and upwardly biased by a spring 286.

A passage 288 senses the pressure in the zone 290 be tween orifice member 276 and valve seat 278 and transmits the zone pressure to the chamber 292 above a diaphragm 294. The lower surface of diaphragm 294 is shown as exposed to atmospheric pressure. Diaphragm 294 operates against the bias of a spring 296 in response to variations in pressure in zone 290 to position a pilot valve 298 disposed in hollow stem 282.

Stem 282 has lateral openings 300 disposed in the chamber 302 between valve seat 278 and outlet 274 and transmits induction passage vacuum from chamber 302 past valve 298 through upper lateral openings 304 to the chamber 306 below diaphragm 284. In operation, as the pressure in zone 290 increases, diaphragm 294 is depressed to open valve 298 and admit induction passage vacuum through openings 304 to chamber 306. Diaphragm 284 is then pulled downwardly against the bias of spring 286 to displace valve member 280 from valve seat 278, thus permitting increased recirculation of exhaust gases. Upon a reduction in pressure in zone 290, spring 296 raises diaphragm 294, thus closing valve 298. The pressure in chamber 306 then increases as air is bled through a slot 308 (in the stem of valve member 298) from the atmospheric chamber 310 between diaphragms 294 and 284. Diaphragm 284 then is pushed upwardly by spring 286 to displace valve member 280 toward valve seat 278, thereby reducing recirculation of exhaust gases. In practice, diaphragms 294 and 284 will move in unison, and the pressure in zone 290 will be held at a substantially constant value.

Another embodiment 62g of control valve assembly 62 is shown in FIG. 9. It comprises a valve body 312 having an upper wall 314, a peripheral wall 316, and a lower wall 318 which define a chamber 320. Valve body 312 has an inlet 321 receiving exhaust gases from first portion 60 of the exhaust recirculation passage. An opening 322 also is formed in valve body 312. A zone 324 is separated from the first portion 60 of the exhaust gas recirculation passage by an orifice member 326 disposed in inlet 321. Valve body 312 also has an outlet 328 discharging exhaust gases to second portion 64 of the exhaust recirculation passage. A downwardly facing valve seat 330 is formed about the inlet side of opening 322.

A valve pintle 332 cooperates with valve seat 330 and may be contoured to provide a variable area for flow of recirculated exhaust gases. Valve pintle 322 is adjustably threaded on a valve stem 334. Stem 334 extends upwardly through an opening 336 in the upper wall 314 of body 312.

A housing member 338 has a central portion 340 provided with an opening 342 receiving valve stem 334.

An intermediate member 344 has an annular, downwardly concave, dished portion 346 disposed between the central portion 340 of housing member 338 and the upper wall 314 of valve body 312. An asbestos insulating disc 350 is received in the dished portion 346 of intermediate member 344 and reduces conduction of exhaust heat from base member 312 to housing member 338.

Intermediate member 344 also has a central, downwardly concave, cupped portion 352 with a central opening 354 receiving valve stem 334. A plurality of graphited asbestos sealing discs 356, supported by a steel washer 358, are received in the cupped portion 352 of intermediate member 344 and engage valve stem 334 to guide stem 334 and to reduce air flow into chamber 320 through openings 354 and 336.

Housing member 338 has an outer rim 360 supported by three outwardly and upwardly extending spokes 362 (only two of which appear in the figure). Each spoke 362 has a slightly raised rib 364 for reinforcement. Spokes 362 provide a minimized path for heat conduction from the central portion 340 of housing member 338 to the rim 360 of housing member 338.

A cover member 366 has a rim 368 secured within rim 360 of housing member 338. A diaphragm 370 is clamped between rims 368 and 360 to define an enclosure 372 between diaphragm 370 and cover 366. Diaphragm 370 carries valve stem 334. A spring 374 exerts an upward bias on diaphragm 370, valve stem 334, and valve pintle 332 to engage valve pintle 332 with valve seat 330.

The pressure in zone 324 between valve seat 330 and orifice member 326 is applied to enclosure 372 through a passage 376 in valve stem 334 and a restricted opening 378 at the tip 380 thereof. Upon an increase in pressure, diaphragm 370 is depressed to displace valve member 332 from valve seat 330, thus permitting increased exhaust gas recirculation. Upon a decrease in pressure, diaphragm 370 is raised to displace valve member 332 toward valve seat 330, thus reducing exhaust gas recirculation. Control valve assembly 62g thus is effective to maintain a constant pressure in zone 324.

In some applications, it may be desirable to employ a very weak spring 374 which will permit unseating of valve pintle 332 when the back pressure is very low 10 inches of water, for example. However, such a construction could permit valve pintle 332 to prematurely engage orifice member 326, thus shutting off recirculation of exhaust gases. In such an application, therefore, it may be desirable to employ a second spring 382, spaced slightly from diaphragm 370, which is engaged by diaphragm 370 after pintle 332 reaches a fully open position at a back pressure of about 30 inches of water, for example. Spring 382 decreases the response of diaphragm 370 to increases in back pressure so that pintle 332 does not engage orifice member 326 and shut off recirculation of exhaust gases until the back pressure reaches a value in the range of eighty to one hundred inches of water, for example.

Spring 374 is seated on a plate 384 which is supported from housing 338 on a member 386. A tang 388 of member 386 extends through a slot 390 in plate 384 and is bent over and retains the lower end of spring 382.

From the foregoing, it will be appreciated that the specific design for control valve assembly 62 may take many different forms and may be operated in numerous ways to achieve the desired result.

I claim:

1. The method of operating an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, and a valve controlling exhaust gas flow through said exhaust gas recirculation passage, said method comprising the steps of operating said valve to create a zone of substantially constant pressure in said exhaust gas recirculation passage,

and flowing exhaust gases through an orifice into said zone,

whereby the rate of exhaust gas flow through said exhaust gas recirculation passage varies in accordance with the exhaust gas pressure in said exhaust passage and is thereby proportional to the rate of air flow through said induction passage.

2. Means for controlling recirculation of exhaust gases in an internal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, said control means comprising means defining an orifice in said recirculation passage, means defining a valve seat in said recirculation passage downstream of said orifice, a valve associated with said valve seat for controlling exhaust gas flow therethrough, and means for positioning said valve to maintain a zone of substantially constant pressure in said recirculation passage between said valve seat and said orifice, whereby exhaust gases may be recirculated from said exhaust passage through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust back pressure and thus is proportional to the rate of air flow through said induction passage.

3. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected to the pressure in the zone between said orifice and said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat, thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

4. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, pressure responsive means connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

5. Means for controlling recirculation of exhaust gases in an internal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, said control means comprising means defining a valve seat in said recirculation passage, a valve associated with said valve seat for controlling exhaust gas flow therethrough, pressure responsive means for positioning said valve, and means for subjecting said pressure responsive means to the differential between the pressure in said exhaust gas recirculation passage upstream of said valve seat and atmospheric pressure whereby upon an increase in such pressure differential said valve is displaced from said valve seat to permit increased recirculation of exhaust gases and whereby upon a decrease in such pressure differential said valve is displaced toward said valve seat to reduce recirculation of exhaust gases.

6. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side to the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat, thereby permitting increase flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat, thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

7. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side of the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, spring means biasing said valve member away from said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat under the bias of said spring means, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat against the bias of said spring means thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant subatmospheric value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

8. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side to the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, spring means biasing said valve member toward said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat against the bias of said spring means, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displce said valve member toward said valve seat under the bias of said spring means, thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant superatmospheric value and exhaust gas may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

9. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second position extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, a pair of coaxially disposed openings having valve seats formed thereabout disposed between said inlet and said outlet, said openings each having an inlet side receiving exhaust gases from said valve body inlet and an outlet side discharging exhaust gases to said valve body outlet, said outlet sides being adjacently disposed and said inlet sides being remotely disposed one from the other, and an orifice formed in said inlet, and a pair of valve members each associated with one of said valve seats for controlling flow of exhaust gases therethrough in a manner substantially unaffected by the effect of the pressure acting on said valve members, pressure responsive means connected to said valve members and responsive to the pressure in the zone between said orifice and said valve seats to displace said valve members from said valve seats upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seats, and to displace said valve members toward said valve seats upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seats, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

10. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, a pair of coaxially disposed openings each having a valve seat formed thereabout disposed between said inlet and said outlet, one of said openings being larger than the other of said openings, and an orifice formed in said inlet, a pair of valve members associated with said valve seats for controlling fiow of exhaust gases therethrough, one of said valve members being larger than the other of said valve members, said one valve member being associated with said valve seat formed about said one opening and said other valve member being associated with said valve seat formed about said other opening, and wherein said other valve member may pass through said one opening for ease of assembly, pressure responsive means connected to said valve members and responsive to the pressure in the zone between said orifice and said valve seats to displace said valve members from said valve seats upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seats, and to displace said valve members toward said valve seats upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seats, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

11. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the inlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

12. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the inlet side of said valve seat means and connected to said valve means are subjected on the side adjacent said valve seat means to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant valve and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

13. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the outlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

14. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

15. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow there-through, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and subjected on the side remote from said valve seat means to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

16. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, a pressure responsive member connected to said valve means and having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet and responsive to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, a second pressure responsive member connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

17. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between siad inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive members disposed on the inlet side of said valve seat means and connected to said valve means, one of said pressure responsive members having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet, the sides of said pressure responsive members adjacent one another being subjected to atmospheric pressure, the opposite side of said one member being subjected to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the opposite side of the other pressure responsive member being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said and thus is proportional to the rate of air flow through said induction passage.

18. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive diaphragms disposed on the inlet side of said valve seat means, a hollow stem connecting said diaphragms to said valve means, one of said diaphragms having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet, the sides of said diaphragms adjacent one another being subjected to atmospheric pressure, the opposite side of said one diaphragm being subjected through said hollow stem to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the opposite side of the other diaphragm being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

19. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction-passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive members disposed on the outlet side of said valve seat means and connected to said valve means, one of said pressure responsive members having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet and having the side thereof adjacent said valve seat means subjected to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the side of said other pressure responsive member remote from said valve seat means being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.

20. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, and control means for positioning said valve means to maintain a substantially constant pressure in the zone between said orifice and said valve seat means, said control means including spring means biasing said valve means toward engagement with said valve seat means, a pressure responsive member connected to said valve means, means defining a vacuum orifice through which said member is subjected to the pressure in said induction passage downstream of said throttle, means defining an air bleed orifice through which said member is subjected to atmospheric air, a bleed valve associated with said vacuum orifice for controlling admission of vacuum therethrough to vary the control pressure created by induction passage vacuum received through said vacuum orifice and atmospheric air received through said air bleed orifice, pressure responsive means connected to said bleed valve and subjected to the pressure in said zone whereby upon an increase in pressure in said zone said pressure responsive means displaces said bleed valve to increase admission of vacuum to said passage means through said vacuum orifice and thereby decreases said control pressure to thereby cause said pressure responsive member to overcome the bias of said spring means and displace said valve means from said valve seat means and increase recirculation of exhaust gases, and second spring means biasing said bleed valve to permit decreased admission of vacuum to said passage means through said vacuum orifice whereby upon a decrease in pressure in said zone said second spring means displaces said bleed valve to decrease admission of air to said passage means through said vacuum orifice and thereby increases said control pressure to thereby permit said first spring means to displace said valve means toward said valve seat means and decrease recirculation of exhaust gases. 

1. The method of operating an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, and a valve controlling exhaust gas flow through said exhaust gas recirculation passage, said method comprising the steps of operating said valve to create a zone of substantially constant pressure in said exhaust gas recirculation passage, and flowing exhaust gases through an orifice into said zone, whereby the rate of exhaust gas flow through said exhaust gas recirculation passage varies in accordance with the exhaust gas pressure in said exhaust passage and is thereby proportional to the rate of air flow through said induction passage.
 2. Means for controlling recirculation of exhaust gases in an internal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, said control means comprising means defining an orifice in said recirculation passage, means defining a valve seat in said recirculation passage downstream of said orifice, a valve associated with said valve seat for controlling exhaust gas flow therethrough, and means for positioning said valve to maintain a zone of substantially constant pressure in said recirculation passage between said valve seat and said orifice, whereby exhaust gases may be recirculated from said exhaust passage through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust back pressure and thus is proportional to the rate of air flow through said induction passage.
 3. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected to the pressure in the zone between said orifice and said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat, thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 4. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gAs recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, pressure responsive means connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 5. Means for controlling recirculation of exhaust gases in an internal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage extending from said exhaust passage to said induction passage downstream of said throttle, said control means comprising means defining a valve seat in said recirculation passage, a valve associated with said valve seat for controlling exhaust gas flow therethrough, pressure responsive means for positioning said valve, and means for subjecting said pressure responsive means to the differential between the pressure in said exhaust gas recirculation passage upstream of said valve seat and atmospheric pressure whereby upon an increase in such pressure differential said valve is displaced from said valve seat to permit increased recirculation of exhaust gases and whereby upon a decrease in such pressure differential said valve is displaced toward said valve seat to reduce recirculation of exhaust gases.
 6. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side to the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat, thereby permitting increase flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat, thereby reducing flow of exhaust gases through said valVe seat, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 7. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side of the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, spring means biasing said valve member away from said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat under the bias of said spring means, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displace said valve member toward said valve seat against the bias of said spring means thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant subatmospheric value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 8. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, and an exhaust passage for exhaust gas flow from the engine, said control valve assembly comprising means defining an exhaust gas recirculation passage having an inlet for receiving exhaust gases from said exhaust passage and an outlet for discharging exhaust gases to said induction passage downstream of said throttle and forming an orifice in said recirculation passage and forming a valve seat in said recirculation passage downstream of said orifice, a valve member associated with said valve seat for controlling exhaust gas flow therethrough, a pressure responsive member connected to said valve member and subjected on one side to the pressure in the zone between said orifice and said valve seat and subjected on the opposite side to atmospheric pressure, spring means biasing said valve member toward said valve seat, said pressure responsive member being responsive to an increase in pressure in said zone to displace said valve member from said valve seat against the bias of said spring means, thereby permitting increased flow of exhaust gases through said valve seat, and being responsive to a decrease in pressure in said zone to displce said valve member toward said valve seat under the bias of said spring means, thereby reducing flow of exhaust gases through said valve seat, whereby the pressure in said zone is maintained at a substantially constant superatmospheric value and exhaust gas may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 9. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second position extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, a pair of coaxially disposed openings having valve seats formed thereabout disposed between said inlet and said outlet, said openings each having an inlet side receiving exhaust gases from said valve body inlet and an outlet side discharging exhaust gases to said valve body outlet, said outlet sides being adjacently disposed and said inlet sides being remotely disposed one from the other, and an orifice formed in said inlet, and a pair of valve members each associated with one of said valve seats for controlling flow of exhaust gases therethrough in a manner substantially unaffected by the effect of the pressure acting on said valve members, pressure responsive means connected to said valve members and responsive to the pressure in the zone between said orifice and said valve seats to displace said valve members from said valve seats upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seats, and to displace said valve members toward said valve seats upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seats, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 10. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, a pair of coaxially disposed openings each having a valve seat formed thereabout disposed between said inlet and said outlet, one of said openings being larger than the other of said openings, and an orifice formed in said inlet, a pair of valve members associated with said valve seats for controlling flow of exhaust gases therethrough, one of said valve members being larger than the other of said valve members, said one valve member being associated with said valve seat formed about said one opening and said other valve member being associated with said valve seat formed about said other opening, and wherein said other valve member may pass through said one opening for ease of assembly, pressure responsive means connected to said valve members and responsive tO the pressure in the zone between said orifice and said valve seats to displace said valve members from said valve seats upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seats, and to displace said valve members toward said valve seats upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seats, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 11. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the inlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 12. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the inlet side of said valve seat means and connected to said valve means are subjected on the side adjacent said valve seat means to the pressure in the zone between said orifice and said valve seat means to displace said valve meaNs from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant valve and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 13. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the outlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 14. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust Gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 15. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow there-through, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pressure responsive member disposed parallel to and on the outlet side of said valve seat means and connected to said valve means and subjected on the side remote from said valve seat means to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 16. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, a pressure responsive member connected to said valve means and having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet and responsive to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, a second pressure responsive member connected to said valve means and responsive to the pressure in the zone between said orifice and said valve seat means to displace said valve means from Said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 17. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between siad inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive members disposed on the inlet side of said valve seat means and connected to said valve means, one of said pressure responsive members having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet, the sides of said pressure responsive members adjacent one another being subjected to atmospheric pressure, the opposite side of said one member being subjected to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the opposite side of the other pressure responsive member being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 18. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valVe seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive diaphragms disposed on the inlet side of said valve seat means, a hollow stem connecting said diaphragms to said valve means, one of said diaphragms having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet, the sides of said diaphragms adjacent one another being subjected to atmospheric pressure, the opposite side of said one diaphragm being subjected through said hollow stem to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the opposite side of the other diaphragm being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 19. An exhaust gas recirculation control valve assembly for use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means and cooperating with the inlet side of said valve seat means to control flow of exhaust gases therethrough, a pair of parallel pressure responsive members disposed on the outlet side of said valve seat means and connected to said valve means, one of said pressure responsive members having an effective area approximately equal to the area of said valve means exposed to the pressure in said outlet and having the side thereof adjacent said valve seat means subjected to the pressure in said outlet to offset the force exerted on said valve means by the pressure in said outlet, the side of said other pressure responsive member remote from said valve seat means being subjected to the pressure in the zone between said orifice and said valve seat means to displace said valve means from said valve seat means upon an increase in pressure in said zone, thereby permitting increased flow of exhaust gases through said valve seat means, and to displace said valve means toward said valve seat means upon a decrease in pressure in said zone, thereby reducing flow of exhaust gases through said valve seat means, whereby the pressure in said zone is maintained at a substantially constant value and exhaust gases may be recirculated through an orifice into a zone of substantially constant pressure to thereby provide recirculation of exhaust gases at a rate which varies in accordance with exhaust gas pressure in said exhaust passage and thus is proportional to the rate of air flow through said induction passage.
 20. An exhaust gas recirculation control valve assembly For use on an internal combustion engine having an induction passage for air flow to the engine, a throttle disposed in said induction passage for controlling air flow therethrough, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage having a first portion extending from said exhaust passage and a second portion extending to said induction passage downstream of said throttle, said control valve assembly comprising a valve body having an inlet for receiving exhaust gases from said first portion of said recirculation passage, an outlet for discharging exhaust gases to said second portion of said recirculation passage, valve seat means formed between said inlet and said outlet, and an orifice formed in said inlet, valve means associated with said valve seat means for controlling flow of exhaust gases therethrough, and control means for positioning said valve means to maintain a substantially constant pressure in the zone between said orifice and said valve seat means, said control means including spring means biasing said valve means toward engagement with said valve seat means, a pressure responsive member connected to said valve means, means defining a vacuum orifice through which said member is subjected to the pressure in said induction passage downstream of said throttle, means defining an air bleed orifice through which said member is subjected to atmospheric air, a bleed valve associated with said vacuum orifice for controlling admission of vacuum therethrough to vary the control pressure created by induction passage vacuum received through said vacuum orifice and atmospheric air received through said air bleed orifice, pressure responsive means connected to said bleed valve and subjected to the pressure in said zone whereby upon an increase in pressure in said zone said pressure responsive means displaces said bleed valve to increase admission of vacuum to said passage means through said vacuum orifice and thereby decreases said control pressure to thereby cause said pressure responsive member to overcome the bias of said spring means and displace said valve means from said valve seat means and increase recirculation of exhaust gases, and second spring means biasing said bleed valve to permit decreased admission of vacuum to said passage means through said vacuum orifice whereby upon a decrease in pressure in said zone said second spring means displaces said bleed valve to decrease admission of air to said passage means through said vacuum orifice and thereby increases said control pressure to thereby permit said first spring means to displace said valve means toward said valve seat means and decrease recirculation of exhaust gases. 